Quantum teleportation over optical fibre is less efficient than over free space, due to the relatively low detection efficiency of typical single-photon detectors that operate at the 1.5 μm low-loss window of optical fibre. Now, Hiroki Takesue and co-workers from NTT Cooperation in Japan and the National Institute of Standards and Technology in the USA have developed MoSi-based superconducting nanowire single-photon detectors (SNSPDs) and used them to demonstrate quantum teleportation over 102 km of optical fibre — four times further than the previous record of 25 km. Time-bin entangled photon pairs were prepared from signal photons (1,546.3 nm) generated through the spontaneous parametric down-conversion process from a periodically poled LiNbO3 waveguide and detected by two SNSPDs. The idler photons (1,555.9 nm) were transmitted over 102 km of dispersion-shifted fibre and detected by another two SNSPDs. The system detection efficiencies of the SNSPDs were 80–86%. The Japanese and American scientists prepared six distinct quantum states for input photons and implemented quantum state tomography on the teleported states. The averaged fidelity for each input state was 83.7%, which relates to a violation of the classical limit by more than eight standard deviations.
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Horiuchi, N. Long-distance teleportation. Nature Photon 9, 707 (2015). https://doi.org/10.1038/nphoton.2015.222